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1988 1500 Brake Lights/ Turn Signal Problem

06-29-2007, 06:16 PM
I had this truck dropped into my lap for the wonderful price of free. It's my old roomate's truck and he didn't want to have anything to do with it after the headgasket went.

Some info on the truck;
1988 Cheyenne 1500
4.3L v6 Automatic
Standard Cab, Longbed.

I'm in dire need of another car since my S10-V8 is in serious need of some TLC and I have school to go to. So I replaced the headgasket and was hunky dory when I fired it up and adjusted the timing. I wanted to make sure everything worked before I plotted down to the DMV and then inspection station to get all the paperwork sorted out and completed.

I flicked on the turn signal, and noticed the relay was on the way out (Flashing twice as fast as normal) "No biggie." I said to myself as I walked around the front to see the turn signals working fine, then walked to the back to see squat. The rear lights are not working when the turn signal is on. "Well crap.." I grab a board and jam it between the brake pedal and the seat to see if the brake lights are working.. nope.. dead too.

I flip the headlights on and do see the rear running lights light up, but alas the brake and turn signals don't work on the rear.

"Too long didn't read.";
Front turn signals work fine, rear turn signals dont.
Stop lights dont work.
Headlights being on/off do not affect above problems.

What I've checked;

Fuse for the Brakes and Signals are good.
Bulbs in the rear are good and get 12v when the headlights are flipped on.
Everything else in the truck works perfectly fine and the rear singal/stop lights worked a few weeks before the truck blew it's headgasket, then just stopped working according to my roomate.

The haynes manual's wiring diagrams are a joke, and i've having some seriously problems tracking this sucker down. I bought a new flasher relay but don't quite know where the junction for it is located. The guy who owned this truck before my roomate did all sorts of horrible things to it (installed his own 3rd party A/C, ugh) so the wiring harness is a little messy but nothing too awful.

Any ideas? If I can get a half way decent wiring diagrams I would be set but the haynes set, and the chlitons (I hate that book) are laughable in their vagueness.

Since that long block of text is kinda well long.. I'll end with some pictures of a the headgasket repair. (
Parked under my friend's half finished barn. (
Let's begin. (
Rubber floor, bench seat. This thing is pretty damn basic. (
Low Miles. (
Tore out alot of the top end, and was working on the heads at this point. (
I can not describe how dirty everything was. Here is the intake manifold with the TBI system. (
One nice thing about this truck is there is a HELL of alot of room to work with. I spent a great deal of my time sitting inside the hood. (
I decided to replace the driver side headgasket as well as preventative maintence. (
Got both heads off. Exhaust bolts are a bitch, and the crosshatching on all cylinders is a little worse for wear. Lobes on the camshaft was washed out. (
The offending headgasket. Wow, thats why the water just POURED out of the engine.

06-29-2007, 06:44 PM
Brake lights and turn signals use the same filiment in the rear lights. Running lights use a different one. So 1st thing to check is for power 12v at the rear light sockets with the brake pedal pushed down. The brake lights also go thru the turn signal switch. If there is a trailer wiring plug on the truck they have been subject to causing these problems also. Let us know.

07-01-2007, 10:22 AM
I would almost guarentee that the brake light circuit boards are shot. This is a big problem on 88/89 trucks. They changed the boards later to take the push in type bulbs. The older ones take the type that push in and turn. That is what I would try first. Unplug them and test the wiring harness for power, then you can test the board for continuity. If you need further explanation let me know. You sound pretty mechanicly inclined (s10 v8, sounds cool always wanted to put a 350 in an astro) BTW, wow, that is a seriously base model truck. I don't think I have ever seen one with the different vents and without the electronic climate control.

07-04-2007, 05:39 PM
I would almost guarentee that the brake light circuit boards are shot. This is a big problem on 88/89 trucks. They changed the boards later to take the push in type bulbs. The older ones take the type that push in and turn.
You are the man, that was it. I hate fiddling with wires and thankfully it was something simple.

It does not have the push and turn type, its the pushin type. But the center light sockets (Turn signal and brake lights) were melted. Replaced them, and its working good as new.


Its a fun little truck, I need to replace the rear end. The stock 4 cylinder rearend (4.10 I think) is way to low. I cruise in top gear doing 55mph turning about 3,000 rpm. The little 283 I have it likes to sing, but driving at that constant rpm drinks gas like crazy.

Here some pics; ( (

07-04-2007, 06:44 PM
I'm putting a 283 in my 88 c1500.

07-04-2007, 11:13 PM
They are good motors if a little down on power compared to a larger displacement, but they scream. I had the option of a built 302 for the same price that was dynoed at 350whp, but I like the sound of a small block winding up to the moon.

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